1. Field of the Invention
This invention relates to oil and gas well-repair equipment, and more particularly, to a method and apparatus for quickly and inexpensively repairing damaged casing of producing oil wells.
2. Description of Related Art
A primary concern in the oil and gas industry is to how to inexpensively repair damaged casing in marginal producing wells. During the production life of a well, corrosion may cause splits, holes or ruptures to form in the well's casing. When undesired fluids, such as water, enter the casing bore through old perforations or damaged casing, the free flow of oil or gas is inhibited or prevented.
For example, in a standard oil and gas well, production tubing is inserted in the casing bore to channel and collect oil and gas from producing perforations. If the casing becomes damaged, undesired fluids may collect between the casing wall and production tubing or within the bore of the production tubing. Accumulation of undesired fluids in either the casing-tubing annulus or production tubing bore creates a hydrostatic pressure sufficient to prevent the free flow of formation fluids into the production tubing.
Traditional methods of isolating old perforations or repairing damaged casing include the use of squeeze cementing and casing patches. Squeeze cementing is a method whereby cement is pumped through the damaged casing at a pressure sufficient to squeeze the water from the cement and leave a cement sheath between the geological formation and the outer surface of the casing. Use of this method, however, causes excess cement to remain inside the casing bore. This excess amount must then be drilled out before the well can be returned to producing status.
The squeeze cement method is inefficient and cost prohibitive for the interested party when faced with the need to repair a marginal producing oil or gas well. A marginal well produces under ten barrels oil equivalent per day and nets approximately $2,000 per month to the party with the working interest. Depending upon the depth of the damaged casing, the cost of a single cement squeeze repair ranges from $35,000 to $50,000. Therefore, it may take approximately seventeen to twenty-five months before a marginal well produces amounts sufficient to recoup repair expenses and enable the interested party to receive a payout.
Alternative repair methods include the use of casing patches. Standard casing patches use packer elements or swab rubbers to straddle the damaged interval of casing. Such methods and apparatus have proven unsatisfactory, however, because these patches may decrease the internal diameter of the well casing, restrict access to the bottom of the well, may not be mechanically set, nor allow for the separate venting of gas through the packer elements.
The present method and apparatus for repairing damaged well casing is cost prohibitive in marginal wells. Therefore, there exists a need for an improved method and apparatus for the repair of oil and gas well casing which enables the interested party to cost effectively and efficiently repair marginally producing wells.